Spray a 13x9 inch pan generously with non-stick cooking spray. Set aside.
Melt butter in a large saucepan over low heat.
Once butter is completely melted add marshmallows to the pan.
Add butterscotch chips to the pan.
Stir continuously until marshmallows and butterscotch chips are completely melted and combined. Remove pan from heat.
Add rice cereal and stir to coat cereal with the marshmallow/butterscotch sauce.
Spoon into prepared 13x9 inch pan.
Use parchment paper to spread out cereal pressing it down into the pan in an even layer.
Allow treats to cool to room temperature, about 15 minutes.
Once treats are completely cooled, turn the pan over onto a cutting board .
Use a sharp knife to cut treats into 12 squares.
Store treats in an airtight container for up to 2 days.